The present invention generally relates to an outlet system communicating between a furnace for melting thermoplastic material and a channel for receiving molten material from the furnace, and more particularly pertains to an outlet system connecting a furnace to a channel means, wherein an electrically conductive refractory conduit is used in conjunction with electrodes in the furnace and channel to supply heat to melt materials near the exit end of the conduit and within the conduit.
Vertically oriented electric glass melting furnaces have been known in the prior art for some time, but it has been only in the last several years that such furnaces have been brought into large scale commercial application. In the more recently developed furnaces, such as the type illustrated in U.S. Pat. Nos. 2,993,079, 3,524,206, 3,583,861, 3,725,558, 3,742,111, and 3,942,968, glass-forming batch materials are fed to the upper end of a vertical chamber and refined molten glass is withdrawn from the bottom of the chamber. High quality glass is thus produced in a single vertical chamber, with melting occuring in an upper portion thereof and preferably some refining occurring in the bottom portion.
The molten glass withdrawn from the electric furnace is received within a laterally extending connector channel situated at the side of the furnace bottom and thereafter is usually directed through a vertical passageway or riser to a mixing chamber and/or a forehearth. For example, in U.S. Pat. No. 3,942,968 to Pieper, the molten glass is withdrawn laterally from the furnace through a connector channel, thereafter is directed through a riser portion where coloring materials may be added, from the riser to a downwardly extending mixing chamber, laterally from the chamber through a second connector channel, then upwardly through a second riser, and finally to a forehearth or feeder. In the Pieper system, the delivery passageway extending from the furnace bottom is formed in refractory block material of the contiguous walls of the furnace and riser, and an electrode is positioned in the passageway. It will be appreciated by those skilled in the art of melting glass that the passageway electrode may not be used when cold glass-forming or batch material surrounds the electrode because the cold material will not be electrically conductive.
In other electric glass-melting furnaces heretofore employed, a refractory metal delivery conduit extends from near the center of the bottom of the furnace to the confines or passageway of the connector channel. The conduit is either placed on the furnace bottom wall or is laid into a trough incorporated in the furnace bottom wall; and the conduit is protected from exposure to solid or liquid contaminants, which originate in the batch and sink through the molten glass, by a cover of refractory blocks. The outlet system of such type of prior art furnace is provided with devices for heating the cold glass-forming material initially within the conduit; because, during the start-up or beginning stages of operation of the furnace, the heat conducted through the conduit from the molten glass in the furnace and connector channel and through the glass-forming or batch materials is not sufficient to melt all the cold batch material initially within the conduit. As used hereinafter, a cold plug is a quantity of batch material or solidified glass which is located within the conduit at a position therein at least generally coterminous with the furnace sidewall portion through which the conduit extends. The cold plug initially obstructs the flow of molten glass from the furnace to the connector.
The devices for heating the cold plug used in the prior known furnaces comprise a first coil-type electric resistance heating element which surrounds the portion of the conduit contained in the furnace sidewall, and a second strip-type electric resistance heating element located at the bottom of passageway of the channel near the exit end of the conduit. These heating devices are very expensive because the strip heater and the parts of the coil heater are made from platinum or a platinum rhodium alloy. Also, the prior art resistance heaters are difficult to install and repair and relatively slow in operation.
The primary object of the present invention is to provide an apparatus for melting a cold plug of batch materials or solidified glass within an outlet conduit which does not require either a coil heater surrounding the conduit or a strip heater in the connector channel, which rapidly melts the cold plug, and which is easy to install and repair.